1. Field of the Invention
The present invention relates to data retransmission method for confirmation information transmissions which may be used for example in communication systems which use communication protocols of OSI (Open Systems Interconnection) reference models. In particular, the present invention relates to a communication confirmation process for a confirmation information transmission service, and this process occurs between layer 2 (the data link layer) and layer 3 (the network layer) when a data transmission in layer 2 is lost. This application is based on patent application No. Hei 8-282662 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
As one communication protocol related to OSI reference models, there is "confirmation information transmission services" which confirm delivery of information transmitted by layer 2, and this is in contrast to "non-confirming information transmission services" which do not confirm delivery of transmitted information. In this confirmation information transmission service, a function for data retransmission during transmission is regulated in layer 2 for situations in which information transmission fails.
As a standard for regulating confirmation information transmission services, for example, there is the digital automobile system standards RCR STD-27D (refer to "The Digital Automobile System Standard Standards RCR STD-27D" Incorporated Foundation of the Radio Wave System Development Center, Jun. 27, 1995, Publication, pages 119.about.120).
Under this standard, in order to transmit data from layer 3 to layer 2, primitives called "DL-Data Requests" and "DL-Data Displays" are regulated, and, by using these primitives, data transmission has been realized. Here, the "DL-Data Request" primitive is used for requesting the transmission of a message using a process of the confirmation information transmission service. In addition, the "DL-Data Display" primitive is for the purpose of indicating the arrival of a received message using the confirmation information transmission service. In this way, in the above-mentioned standard, with regard to data transmission from layer 3 to layer 2, there is no regulation at all of primitives for the purpose of conducting confirmation of delivery of transmitted information.
FIG. 3 shows the structure of layers in the OSI reference model. The information receiving side and transmitting side each have a layer 1, a layer 2 and a layer 3. Here, layer 1 is a physical layer for carrying out electrical and physical control. Communication layer 2 is a data link layer and carries out transmission of layer-3-data in the logic link layers. Layer 3 is the network layer and carries out call control such as call setting and call release. In addition, the interface LI between layers regulates the method of data transmission between layer 2 and layer 3. Moreover, in the OSI reference model, there may be a plurality of layers having positions higher than layer 3, but since they have no direct relationship with the present invention, these higher position layers are not shown in FIG. 3.
Next, with reference to FIG. 4, a data retransmission method relating to a confirmation information transmission which uses related art will be explained.
Firstly, at time t1, Data D1 (layer-3-data) is transmitted from layer 3 to layer 2. If this is done, at time t2, layer 2 begins timer observations for the purpose of detecting the loss of the transmission, and simultaneously transmits data ("confirmation data" in the Figure) to layer 1. If this transmission is successful, at time t3, layer 1 returns a reply corresponding to this transmission to layer 2. When this reply is received by layer 2, at time t4, layer 2 recognizes that the transmission to layer 1 has been successful and the timer observation which began at time t2 is terminated.
Next, at time t5, Data D2 which is different from Data D1 is transmitted from layer 3 to layer 2. If this is done, in the same way as mentioned above, layer 2 begins timer observation at time t6 and simultaneously transmits confirmation data to layer 1. Then, if transmission of data from layer 2 to layer 1 fails, layer 2 cannot receive a response to this transmission from layer 1. Due to this, layer 2 recognizes that the transmission of data has failed by means of the timer observation, then a procedure for retransmission of the confirmation data is carried out. Then, if this retransmission procedure also fails, at time t7, layer 2 discards the Data D2 which was transmitted from layer 3. In addition, at this time, by means of resetting itself, layer 2 shifts to a condition in which the link is not established. When these procedures are completed, the condition of layer 2 returns to the normal condition, and transmission of data becomes possible again.
Next, at time t8, if data D3 is transmitted from layer 3 to layer 2, in the same way as mentioned above, at time t9, layer 2 begins timer observation and transmits confirmation data to layer 1. Then, in the same way as in the transmission of D1, if the transmission of data D3 is successful, layer 1 returns a reply to layer 2 at time t10. By means of this, at time t11, layer 2 recognizes the success of the transmission and timer observation is terminated.
In the above-mentioned way, layer 3 recognizes the transmission of Data D1, Data D2 and Data D3 as all being complete. However, in reality, the Data D2 which failed in transmission was discarded in layer 2. As a result, for the layer-3-data receiving side (FIG. 3), Data D2 remains lost, and only Data D1 and data D3 have been received.
In other words, in the data retransmission method of the related art, with regard to situations in which the retransmission procedures of layer 2 fail, there is no consideration whatsoever to an error recovery process in which, for example, layer 3 which is a higher position layer carries out retransmission. For this reason, when the retransmission process conducted in layer 2 fails, layer 2 is left in a condition in which data has been discarded, loss of data occurs, and this is a big problem with regard to reliability.